A balance chemical equation is an equation describing a chemical reaction with the right number of molecules to cancel out each side of the equation.
For example:
H2 + O2 —> H2O
Make sure the number of molecules in your reactants equal the number of molecules in your product
2H2 + O2 —> 2H2O
(4 hydrogens and 2 oxygens = 4 hydrogens and 2 oxygens)